Refrigerant System With Stator Heater

ABSTRACT

A refrigerant system adapted to reduce refrigerant migration therein includes a compressor and a controller. The compressor has a motor with motor windings. The motor windings are responsive to control signals to selectively generate heat in a manner that does not turn the motor. The controller selectively energizes the motor windings to generate heat based on at least one of a monitored temperature or pressure to warm the compressor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional patent application which claims the benefit of U.S. provisional patent application Ser. No. 61/251,424 filed Oct. 14, 2009, the entire contents of which are incorporated herein by reference.

BACKGROUND

The present invention relates to refrigerant heating and/or cooling systems, and more particularly, to a heating and/or cooling system with a stator heater integral to a compressor to prevent the migration of liquid refrigerant to the compressor.

Heating, ventilating and air conditioning (HVAC) systems and refrigeration systems (collectively commonly called refrigerant systems) can be used in a variety of applications to heat and/or cool desired units or areas. More particularly, HVAC systems and refrigeration systems operate in a number of different refrigeration cycles. For example, if the HVAC system employs a heat pump, the system can operate in a vapor-compression refrigeration cycle to provide cooling to an indoor unit. In the vapor-compression refrigeration cycle, an outdoor unit with a first heat exchanger (condenser) is coupled to a compressor which circulates liquid refrigerant to a second heat exchanger (evaporator) located in the indoor unit.

Most refrigeration cycles experience a tendency for liquid refrigerant to try to migrate through the liquid line between the indoor heat exchanger and the outdoor heat exchanger when the compressor is not in operation. This phenomena is due to natural convection, which causes the refrigerant to flow within the refrigerant system and migrate to the coldest point in the system. The relatively large thermal mass of the compressor causes it to be the coldest point in the refrigerant system. When refrigerant migration occurs, some of the liquid refrigerant moves into the compressor, settling in the oil sump located at the bottom of the compressor. When the compressor is next operated, the liquid refrigerant boils into a gaseous state and exits the compressor. Unfortunately, when this occurs the refrigerant carries a portion of the compressor oil with it. This process reduces the amount of lubricant in the compressor. The loss of this oil may cause increased wear and can detrimentally affect the reliability and life of the compressor especially in larger refrigerant systems that employ larger volumes of refrigerant and operate for longer periods of time.

SUMMARY

A refrigerant system adapted to reduce refrigerant migration therein includes a compressor and a controller. The compressor has a motor with motor windings. The motor windings are responsive to control signals to selectively generate heat in a manner that does not turn the motor. The controller selectively energizes the motor windings to generate heat based on at least one of a monitored temperature or pressure to warm the compressor.

A method of that reduces refrigerant migration to a compressor includes the compressor which has a motor with motor windings responsive to control signals to selectively generate heat in a manner that does not turn the motor. A controller monitors at least one of a temperature or pressure and controls the motor windings to selectively generate heat based on at least one of the monitored temperature or pressure to reduce or eliminate refrigerant migration to the compressor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic illustration of a refrigerant system arranged as a heat pump operating in a cooling mode.

FIG. 1B is a schematic illustration of the heat pump of FIG. 1A operating in a heating mode.

FIG. 2A is a schematic illustration of another heat pump utilizing an air cooled inverter drive and operating in a cooling mode.

FIG. 2B is a schematic illustration schematic illustration of the heat pump of FIG. 2A operating in a heating mode.

FIG. 3 is a side view of one embodiment of a compressor with a refrigerant cooled inverter drive from FIGS. 1A and 1B.

FIG. 4 is a cross-sectional view of the compressor illustrating interior components including a motor.

FIG. 5A is a perspective view of one embodiment of a stator portion of the motor.

FIG. 5B is a perspective view of a single stator portion.

FIG. 5C is a perspective view of one embodiment of a rotor portion of the motor.

FIG. 5D is an exploded view of the rotor portion of FIG. 5B.

FIG. 6 is a flow chart illustrating a method of controlling a stator to produce heat within the compressor and avoid overheating the inverter drive.

DETAILED DESCRIPTION

The present application relates to a refrigerant system and methods of controlling the refrigerant system when the refrigerant system is in an off mode to keep refrigerant from migrating to the refrigerant system's compressor. In particular, the refrigerant system includes a compressor having motor windings responsive to control signals to selectively generate heat that keeps refrigerant from migrating to the compressor as a result of natural convection. The motor windings generate heat in a manner that does not turn the motor (i.e., heat is generated by the motor in a manner that does not drive the compressor to compress refrigerant). The refrigerant system also includes a controller that selectively energizes the motor windings to generate the heat based on at least one of a monitored temperature or pressure.

The methods disclosed control the amount, frequency and duration of heat produced by the motor windings of the compressor. The methods also protect the electrical components of an inverter device from an overheat condition that can result from heating the compressor when the compressor is in the off mode.

FIG. 1A is a schematic illustration of a refrigerant system 10A arranged as a heat pump 12A operating in a cooling mode. FIG. 1B is a schematic illustration of the heat pump 12A operating in a heating mode. Heat pumps 12A are one of a variety of refrigerant systems 10A used to provide heating or cooling to an indoor unit 14. A portion of the heat pump 12A extends into an outdoor unit 16 for heat exchange purposes. The indoor unit 14 and outdoor unit 16 are connected by a first conduit or flow path 18 and a second conduit or flow path 20. In addition to the first conduit 18 and the second conduit 20, the heat pump 12A includes a first heat exchanger 22 having a first port 24 and a second port 26, a first expansion device 27, a first air circulation device 28, a second heat exchanger 30 having a first port 32 and a second port 34, a second air circulation device 36, a reversing valve 38 with a main body portion 40, an accumulator 42, a compressor and drive subassembly 44A with a refrigerant cooled inverter drive 46A and a compressor 48. The compressor 48 includes a suction port 50, a discharge port 52, and a motor stator 54. The heat pump 12A also includes a sensor array 56. This array 56 includes a motor stator temperature sensor 58, an inverter module temperature sensor 60, an internal compressor temperature sensor 62, an outdoor air temperature sensor 64, an outdoor coil temperature sensor 66, an outdoor suction temperature sensor 68, an indoor air temperature sensor 70, and an outdoor suction pressure sensor 72. Transmission media 74 or wireless media transmit signals (digital or analog) to a subassembly controller 76 or system controller 78 from the sensors 58, 60, 64, 66, 68, 70, 72 and the other components of the refrigerant system 10A.

The first heat exchanger 22 is positioned within the indoor unit 14. The first heat exchanger 22 fluidly communicates with the first conduit 18 and the second conduit 20 through the first port 24 and the second port 26, respectively. The first expansion device 27 is disposed in fluid communication with the second conduit 20 between the first heat exchanger 22 and the second heat exchanger 30 and can be disposed in either the indoor unit 14 or the outdoor unit 16. The first air circulation device 28, such as a fan is disposed within the indoor unit 14. The air circulation device 28 is arranged to move air over and/or around the first heat exchanger 22 and circulate air within the indoor unit 14. This allows for improved transfer of thermal energy either to or from the first heat exchanger 22 to the indoor unit 14.

The first conduit 18 and the second conduit 20 extend from the indoor unit 14 to the outdoor unit 16. More particularly, the first conduit 18 fluidly communicates with the reversing valve 38 and the second conduit 20 fluidly communicates with the second heat exchanger 30 through the first port 32. Thus, the first heat exchanger 22 fluidly communicates with the second heat exchanger 30. The second heat exchanger 30 is disposed within the outdoor unit 16 and fluidly communicates with the reversing valve 38 through the second port 34. The second air circulation device 36 is disposed adjacent the second heat exchanger 30 to move ambient air over or past the second heat exchanger 30 to either add or remove heat from the system 10A.

The reversing valve 38 (also known as a four-way valve) is fluidly coupled between the first and second heat exchangers 22 and 30 and the compressor and drive subassembly 44A. The main body portion 40 of the reversing valve 38 rotates between a first position for cooling mode (FIG. 1A) to a second position for heating mode (FIG. 1B). In the first position as illustrated in FIG. 1A, the main body portion 40 fluidly couples the second port 34 of the second heat exchanger 30 to the compressor 48 and couples the first conduit 18 to the accumulator 42. When rotated to the second position as illustrated in FIG. 1B, the main body portion 40 fluidly couples the second port 34 to the accumulator 42 and couples the first conduit 18 to the compressor 48. Thus, by rotating the main body portion 40, the reversing valve 38 can either direct the refrigerant discharged from the compressor 48 to either the second heat exchanger 30 in the cooling mode (FIG. 1A), or to the first conduit 18 in the heating mode (FIG. 1B).

In FIGS. 1A and 1B, the compressor and drive subassembly 44A is disposed in fluid communication with the accumulator 42 along the suction line 43. More specifically, the inverter drive 46A is arranged in fluid communication on the suction line 43 with the accumulator 42 and with the compressor 48 via suction port 50. Refrigerant passes through the compressor 48 and is compressed to a higher pressure before being discharged through the discharge port 52 into discharge line 53. Compressor 48 commonly utilizes an internal motor (not shown) to convert electrical energy to mechanical energy and thereby achieve compression of the refrigerant. As will be discussed in greater detail subsequently, the motor has a stator 54 configured to selectively act as a heater to reduce or eliminate fluid migration to the compressor 48 that would otherwise occur during periods of nonuse of the compressor 48 due to natural convection.

The sensor array 56 is distributed in various locations throughout the heat pump 12A. In the embodiment shown in FIGS. 1A and 1B, the sensor array 56 gathers data relating to at least one of the system temperatures and/or pressures and outputs this data as signals to the subassembly controller 76 or system controller 78 via transmission media 74. The subassembly controller 76 and/or system controller 78 monitors the signals supplied by the senor array 56 and controls components of the refrigerant system 10A, including the motor stator 54 to achieve selective heating. In the embodiment shown in FIGS. 1A and 1B, the sensor array 56 includes the motor stator temperature sensor 58, the inverter module temperature sensor 60, the internal compressor temperature sensor 62, the outdoor air temperature sensor 64, the outdoor coil temperature sensor 66, the outdoor suction temperature sensor 68, the indoor air temperature sensor 70, and the outdoor suction pressure sensor 72.

100261 In the embodiment shown, the motor stator temperature sensor 58 is disposed within or adjacent motor stator 54 within the compressor 48. The motor stator temperature sensor 58 signals the subassembly controller 76 via transmission medium 74. The inverter module temperature sensor 60 is disposed within the inverter device 46A. The internal compressor temperature sensor 62 is disposed within the compressor 48 adjacent a compression area therein. In the embodiment shown, the compressor 48 is a scroll type compressor, and therefore internal compressor temperature sensor 62 would be disclosed next to the scroll of the compressor 48. Similar to the motor stator temperature sensor 58, in one embodiment both sensors 60 and 62 signal the subassembly controller 76 via transmission media 74. In the embodiment shown in FIG. 1A and FIG. 1B, subassembly controller 76 has the ability to monitor signals from sensors 58, 60 and 62 and control various components of the refrigerant system 10A. In particular, subassembly controller 76 can control the inverter device 46A, and thus, the compressor 48 operation and speed. Additionally, the subassembly controller 76 is capable of selectively energizing the windings of the motor stator 54 to generate heat based on at least one of the motor stator temperature, the inverter module temperature and the internal compressor temperature signals. Alternatively, the subassembly controller 76 can output signals (analog or digital) corresponding to the motor stator temperature, the inverter module temperature and the internal compressor temperature to the system controller 78. In this instance, the system controller 78 monitors these signals and signals from the other sensors 64, 66, 68, 70 and 72 and controls various components of the refrigerant system 10A including the motor windings to selectively generate heat within the compressor 48 as discussed previously. Thus, the system controller 78 selectively energizes the motor windings to generate heat based on at least one of the monitored signals received by the controller 78 from the sensors 58, 60, 62, 64, 66, 68, 70 and 72. In other embodiments, the subassembly controller 76 can be eliminated entirely in favor of the assembly control 78.

The outdoor air temperature sensor 64 can comprise a thermostat, thermistor or thermocouple and can be disposed anywhere within the outdoor unit 16. However, in one embodiment outdoor air temperature sensor 64 is disposed within the unit which houses the system controller 78. The outdoor coil temperature sensor 66 can comprise a thermistor clipped or otherwise mounted to a coil tube of the second heat exchanger 30. The outdoor suction temperature sensor 68 can comprise a thermistor attached to the suction line 43 adjacent the accumulator 42. The indoor air temperature sensor 70 is disposed within the indoor unit 14. Additionally, a sensor (not shown) for measuring the indoor unit return air temperature can be utilized in the refrigerant system 10A. The outdoor suction pressure sensor 72 can comprise a transducer disposed in the suction line 43 adjacent to the suction temperature sensor 68. The sensors 58, 60, 62, 64, 66, 68, 70 and 72 output data signals via the transmission medium 74 which can comprise, for example, wiring, coaxial or fiber optic cable, wireless, radio and infrared signals, or any conductor capable of carrying an electrical signal.

In controlling the various components of the refrigerant system 10A, system controller 78 accepts data from the sensors 58, 60, 62, 64, 66, 68, 70 and 72, the inverter device 46A, the compressor 48, and various other components, and executes programs for the purpose of comparing the data to predetermined operational parameters. Several programs compare the operational parameters to predetermined variances (e.g., low temperature, high temperature, low pressure) and if the predetermined variance is exceeded, the system controller 78 generates a signal that may be used to indicate an alarm or may initiate other control methods that change the operation of the heat pump 12A such as reducing or turning on or off energy to the motor windings within the compressor 48.

The subassembly controller 76 and the system controller 78 comprise any suitable electronic device capable of accepting data and executing the instructions to process the data. The controllers 76 and 78 may have a display for presenting the results and/or receiving instructions. Alternatively, the controllers 76 and 78 can accept instructions through, for example, electronic data card, voice activation means, manually-operable selection and control means and electronic or electrical transfer. The subassembly controller 76 and the system controller 78 can be, for example, a microprocessor, a microcomputer, a minicomputer, an optical computer, a board computer, a complex instruction set computer, an ASIC (application specific integrated circuit), a reduced instruction set computer, an analog computer, a digital computer, a solid-state computer, a single-board computer, a buffered computer, a computer network, a desktop computer, a laptop computer, or a hybrid of any of the foregoing.

During the cooling mode of operation shown in FIG. 1A, the main body portion 40 of the reversing valve 38 fluidly couples the second port 34 of the second heat exchanger 30 to the compressor 48 and couples the first conduit 18 to the accumulator 42. In this manner, the refrigerant pressurized in the compressor 48 flows through the discharge line 53 and reversing valve 38 to the second heat exchanger 30 which operates as a condenser to condense the high pressure vapor into liquid thereby extracting heat from the refrigerant to the outdoor unit 16. From the second heat exchanger 30 the refrigerant flows to the expansion device 27 which throttles the flow of refrigerant lowering its pressure. The expansion device 27 can comprise, for example, an expansion valve or a capillary tube. The refrigerant then flows to the first heat exchanger 22 which operates as an evaporator to evaporate the refrigerant to gas thereby transferring heat from the indoor unit 14 to the refrigerant. The refrigerant continues flowing from the first heat exchanger 22 through the first conduit 18 and the reversing valve 38 to the accumulator 42. The accumulator 42 uses an inverted trap to attempt to protect the compressor 48 from liquid refrigerant in the suction line 43. From the accumulator 42, the gas refrigerant is drawn by the compressor 48 along the suction line 43 through the inverter 46A to suction port 50.

When operating the heating mode shown in FIG. 1B, the direction of refrigerant flow within the first conduit 18 and the second conduit 20 is reversed. This is accomplished by the main body portion 40 of reversing valve 38 which rotates to fluidly couple the second port 34 of the second heat exchanger 30 to the accumulator 42. The rotation of the main body portion 40 also fluidly couples the first conduit 18 to the discharge line 53 to the compressor 48. In the heating mode, the first heat exchanger 22 operates as a condenser to warm the inner unit 14. Conversely, the second heat exchanger 30 operates as an evaporator.

Heat pump 10B illustrated in FIGS. 2A and 2B has components similar to and operates in a manner similar to the heat pump 10A illustrated in FIGS. 1A and 1B. The heat pump 10B differs in that it employs an air cooled inverter drive 46B, and thus, the inverter drive 46B is not connected to the suction line 43. In the embodiment illustrated in FIGS. 2A and 2B, the inverter drive 46B does not have a housing so its components are cooled by the second air circulation device 36. Alternatively, the inverter drive 46B components can be cooled by a dedicated fan within the outdoor unit 16. In one embodiment, the presence of an overheat condition within the air cooled inverter drive 46B can be measured by taking the temperature within the outdoor unit 16 either/both prior to and after the second heat exchanger 30 with outdoor air temperature sensors 64A and 64B. As will be discussed in further detail subsequently, the subassembly controller 76 or the system controller 78 can be configured to control operation of the second air circulation device 36 or dedicated fan (turn the second air circulation device 36 on and off) to selectively move cooling air across the electronic components of the inverter drive 46B. In this manner, the electronic components within the inverter drive 46B can be cooled. In an alternative embodiment, the inverter drive 46B can include the inverter module temperature sensor 60 disposed within or adjacent the inverter device 46B to sense the overheat condition.

FIG. 3 is a side view of the compressor and drive subassembly 44A with a housing removed. In FIG. 3, the suction line 43 and the discharge line 53 fluidly connect the compressor and drive subassembly 44A to the remainder of the refrigerant system 10A (FIGS. 1A and 1B). More particularly, the suction line 43 fluidly connects the accumulator 42 (FIGS. 1A and 1B) to the inverter drive 46A. The suction line 43 extends through the inverter drive 46A to fluidly connect the inverter drive 46A with the compressor 48 via the suction port 50. The compressor 48 pressurizes the refrigerant received therein and discharges the refrigerant to the discharge line 53 through the discharge port 52.

As will be discussed in further detail subsequently, the compressor 48 can be selectively operated by the subassembly controller 76 (FIGS. 1A and 1B) or the system controller 78 (FIGS. 1A and 1B) to allow refrigerant to flow through the inverter drive 46A. In this manner, the refrigerant can be used to cool the electronic components within the inverter drive 46A and alleviate the overheat condition. Additionally, inverter drive 46A may include a device such as a cold plate (not shown). The refrigerant cools the cold plate prior to entering compressor 48 and thereby cools the electrical components of the inverter drive 46A. The cold plate functions as a heat exchanger between the refrigerant and the inverter drive 46A so that heat from inverter drive 46A is transferred to refrigerant prior to the refrigerant entering the compressor 48.

The compressor 48 is driven by the inverter drive 46A, also commonly referred to as a variable frequency drive (VFD). As illustrated in FIG. 3, the inverter drive 46A can be housed within an enclosure 80. The inverter drive 46A is disposed adjacent the compressor 48 and receives electrical power from a power supply via a power cable 82A and delivers electrical power to compressor 48 via a second power cable 82B connected to a terminal box (not shown) that is also connected to the compressor 48. As previously discussed, inverter drive 46A can include the subassembly controller 76 (not shown) which can be housed within or outside the inverter drive 46A. If utilized, the subassembly controller 76 would include a processor and software operable to modulate and control the frequency of electrical power delivered to the electric motor of compressor 48. The subassembly controller 76 also would include a computer readable medium for storing data including the software executed by the processor to modulate and control the frequency of electrical power delivered to the electric motor of the compressor 48 and the software necessary for subassembly controller 76 to execute and perform the protection and control algorithms of the present teachings. In particular, subassembly controller 76 would be capable of performing the functions discussed previously such as monitoring data signals from various sensors and selectively energizing or de-energizing the windings within the compressor 48 to generate heat or stop the generation of heat based on the monitored signals. By modulating the frequency of electrical power delivered to the electric motor of compressor 48, the subassembly controller 76 (or system controller 78) can thereby modulate and control the speed, and consequently the capacity, of the compressor 48.

The inverter drive 46A includes solid state electronics to modulate the frequency of electrical power. Generally, the inverter drive 46A converts the inputted electrical power from AC to DC, and then converts the electrical power from DC back to AC at a desired frequency. For example, inverter drive 46A can directly rectify electrical power with a full-wave rectifier bridge. The inverter driver 46A can then chop the electrical power using insulated gate bipolar transistors (IGBT's) or thyristors to achieve the desired frequency. Other suitable electronic components can be used to modulate the frequency of electrical power from power supply. The speed of the electric motor driving the compressor 48 is controlled by the frequency of electrical power received from the inverter driver 46A.

FIG. 4 is a cross-sectional view of the compressor 48 illustrating various interior components. The suction port 50 is not visible to the viewer from the cross-section of the compressor 48. In addition to the motor stator 54, the motor stator temperature sensor 58, the internal compressor temperature sensor 62, and the discharge port 52, the compressor 48 includes a motor 86 with a rotor 88, a drive shaft 90 and a scroll 92.

In the embodiment shown in FIG. 4, the compressor 48 comprises a conventional scroll type compressor; however, the invention disclosed herein is equally applicable to reciprocating type, rotary screw and rotary vane type compressors. The motor 86, comprising the motor stator 54 and rotor 88, is disposed within the compressor 48 to convert electrical power into mechanical work. In particular, the motor 86 is configured to receive electrical power from the inverter drive 46A or 46B (FIGS. 1A, 1B, 2A and 2B) and rotate the rotor 88 and the drive shaft 90 to which the rotor 88 is coupled. The motor stator 54 remains stationary adjacent the rotor 88. The rotation of the drive shaft 90 draws refrigerant into the compressor 48 and distributes lubricating oil from a reservoir in a lower portion of the compressor 48. The drive shaft 90 is connected to the scroll 92 which uses two interleaved spiral scrolls to compress the refrigerant drawn in to the compressor 48. After compression in the scroll 92, the refrigerant is discharged through the discharge port 52 to the discharge line 53 (FIGS. 1A, 1B, 2A and 2B). The motor stator temperature sensor 58 is disposed adjacent to or within the motor stator 54 and outputs signals corresponding to sensed temperature to the subassembly controller 76 or system controller 78 (FIGS. 1A and 1B). The internal compressor temperature sensor 62 is disposed adjacent the scroll 92 and outputs signals corresponding to sensed temperature to the subassembly controller 76 or the system controller 78.

When the refrigerant system 10A or 10B (FIGS. 1A, 1B, 2A and 2B) is not in operation, the motor 86 does not rotate the drive shaft 90 and the compressor 48 does not compress the refrigerant. To avoid or reduce refrigerant migration to the compressor 48 in this off state due to natural convection (i.e., the tendency of a fluid such as a refrigerant to move from one location to another due to density differences in the fluid occurring because of temperature gradients between the locations), the subassembly controller 76 or the system controller 78 is configured to control the inverter 46A or 46B to selectively energize the windings within the motor stator 54 to generate heat within the compressor 48. More particularly, in one embodiment the motor 86 is a brushless permanent magnet motor, also commonly known as a permanent magnet synchronous motor. During the time period when refrigerant system 10A or 10B and compressor 48 are not in operation, and during a predetermined warm up period after system 10A or 10B startup, the inverter drive 46A or 46B is selectively controlled to provide varying levels of power to the motor windings in such a manner so as not to cause rotation (i.e., turn) of the rotor 88. In particular, if a three-phase power supply is employed, a single-phase current may be applied to the windings within the motor stator 54. The resistance of the windings causes the windings to generate heat. The heat generated keeps the compressor 48 from being the heat sink for the system 10A or 10B, thus migration of the refrigerant to compressor 48 is avoided.

FIGS. 5A-5D illustrate the motor stator 54 and the rotor 88. Additionally, the motor stator 54 includes laminated segments 94 with coil windings 96. The rotor 88 includes a main body 98, magnets 100, end caps 102 and fasteners 104.

In the embodiment shown, the motor stator 54 comprises a conventional segmented stator for a brushless permanent magnet motor. The construction and operation of a similar motor stator and rotor for a permanent magnet motor is further detailed in U.S. Pat. No. 7,122,933 to Horst et al., which are herein incorporated by reference.

In particular, the laminated segments 94 can be individually assembled and subsequently combined to define the motor stator 54. The laminated segments 94 are connected to define a circuit in a manner known in the art. As illustrated, each laminated segment 94 has the coil windings 96 disposed therein. In one embodiment, the coil windings 96 are wound as single-layer or double-layer concentrated windings to define three phases. The illustrated embodiment has nine laminated segments 94 and nine coil windings 96. The leads (not shown) of each coil winding 96 are electrically connected such that the three phases induce alternating eddy currents when an electrical current is applied. If current in a proper phase (e.g., in this example three phase) is applied, the eddy currents induce rotation of the rotor 88. Although illustrated with nine coil windings 96 it is anticipated in other embodiments that a different number of coil windings could be used.

When assembled, the main body 98 of the rotor 88 is disposed adjacent the interior of the laminated segments 94. The main body 98 is adapted to receive the drive shaft 90 therein. The main body 98 is also adapted to receive the magnets 100. The end caps 102 and fasteners 104 secure the magnets 100 within the movable rotor 88. In the embodiment shown, six magnets having six poles can be disposed within the main body 98. In other embodiments a different number of magnets can be used.

FIG. 6 is a flow chart illustrating one method 200 of controlling the motor stator 54 to produce heat within the compressor 48 to keep refrigerant from migrating therein. The method 200 protects the electrical components of the inverter module 46A or 46B from an overheat condition that can result from the stator heating of the compressor 48.

The method 200 starts at block 202 and proceeds to query block 204. Query block 204 determines whether the compressor 48 (FIGS. 1A-4) is in an off mode where the compressor 48 is not in operation. The off mode includes a warm up or start up mode for the compressor 48. If the compressor is in the off mode, the method 200 proceeds to block 206. In block 206, a check of the temperature sensed within the compressor 48 and/or the inverter device 46A or 46B is performed periodically using one or more of the sensors 58, 60, and/or 62 (FIGS. 1A, 1B, 2A and 2B). Alternatively or in addition thereto, the outdoor air temperature can be monitored using the outdoor air temperature sensor 64. The frequency at which the temperatures are monitored can be varied based on whether the temperatures fall within a predetermined range of temperatures. For example, in one embodiment if the sensed outdoor air temperature is greater than about 55° F. (13° C.) the outdoor air temperature sensor 64 is checked every 50 minutes, if the sensed outdoor air temperature is greater than about 20° F. (−7° C.) and less than about 55° F. (13° C.) the outdoor air temperature sensor 64 is checked every 30 minutes, and if the outdoor air temperature is less than about 20° F. (−7° C.) the outdoor air temperature sensor 64 is checked every 30 seconds.

In one embodiment, query block 208 determines whether the temperature within the inverter device 46A or 46B (as sensed by the inverter module temperature sensor 60) is greater than a minimum inverter temperature. In one embodiment, the minimum inverter temperature is about 0° F. (−18° C.) or below. In another embodiment shown in FIGS. 2A and 2B, one or both outdoor air temperature sensors 64A and 64B can be utilized to calculate the temperature within the inverter device 46B. If the temperature of the inverter device 46A or 46B is above the minimum inverter temperature, the method 200 proceeds to query block 210. Query block 210 determines whether the temperature within the compressor 48 (as sensed by the motor stator temperature sensor 58 or the internal compressor temperature sensor 62) exceeds a minimum internal compressor temperature. In one embodiment, the minimum internal compressor temperature is in a range of between about −20° F. (−29° C.) and 20° F. (31 7° C.). If the temperature within the inverter device 46A or 46B is below the minimum inverter temperature or the temperature within the compressor 48 is less than the minimum internal compressor temperature the method 200 proceeds to block 212.

In block 212, the compressor 48 is locked out for a period of time such that the compressor 48 is restricted from operating until both the temperature within the inverter device 46A or 46B and temperature within the compressor 48 exceed the minimums. During the lockout period of block 212 and for the period indicated in block 214 the windings of the motor stator 54 are energized to produce heat within the compressor 48. Power can be supplied to the windings of the motor stator 54 at various levels to produce various modes of heating within the compressor 48. In block 214, power is supplied to the windings of the motor stator 54 at a higher level than a lower power level which will be discussed subsequently. In one embodiment, the motor stator 54 is supplied with 50 Watts of power, however, the amount of power necessary to produce adequate heating of the system will vary depending on system criteria.

If the temperature within the inverter device 46A or 46B is above the minimum inverter temperature and the temperature within the compressor 48 is above the minimum internal compressor temperature the method 200 advances to query block 216. Query block 216 determines whether the temperature within compressor 48 is the coldest part of the refrigerant system 10A or 10B. In one embodiment, this inquiry is conducted by comparing the temperature sensed by the motor stator temperature sensor 58 or the internal compressor temperature sensor 62 to either a minimum outdoor air temperature and/or a minimum indoor air temperature. If the temperature within the compressor 48 is colder than either the minimum indoor air temperature or the minimum outdoor air temperature, than the compressor 48 is the coldest part of the refrigerant system 10A or 10B (and therefore there is a danger of refrigerant migration thereto) and stator heating to warm the compressor 48 is required. Thus, if the compressor 48 is the coldest part of the refrigerant system 10A or 10B, the method 200 proceeds to block 214 where the compressor 48 is warmed. In one embodiment, the minimum outdoor air temperature is below 0° F. (−18° C.) and the minimum indoor air temperature is below 65° F. (18° C.).

After the period of heating in block 214, the method 200 advances to query block 218 which determines whether the inverter drive 46A or 46B is overheating. In one embodiment, the temperature within the inverter drive 46A or 46B can be ascertained in the manner used in block 208. A temperature limit used in query block 218 will vary depending on the components used by the inverter drive 46A or 46B and a safety factor temperature offset used. If the sensed and/or calculated temperature within the inverter drive 46A or 46B exceeds the temperature limit minus the temperature offset, the method 200 proceeds to query block 220.

Query block 220 determines whether the inverter drive is a refrigerant cooled inverter 46A or an air cooled inverter 46B. If the inverter drive is the refrigerant cooled inverter 46A, the method 200 advances to query block 222 which determines if the inverter temperature exceeds the temperature limit minus the temperature offset by a predetermined temperature value. Although the range of temperatures for the predetermined value may vary, in one embodiment if the predetermined value (temperature interval) is in excess of about 10° F. (>5.6° C.), the method 200 goes to block 224 where the amount of power to the windings of the motor stator 54 is reduced to a lower level. If the predetermined value (temperature interval) is between about 0° F. and 10° F. (0° C. and 5.6° C.), the method 200 goes to block 226 where the windings of the motor stator 54 are de-energized completely so that they do not produce heat within the compressor 48. In the embodiment shown in FIG. 6, the method 200 advances from block 226 to a “bump start” mode of operation in block 228. The “bump start” mode cycles the compressor 48 operationally on and off to circulate refrigerant through the refrigerant cooled inverter drive 46A, and thereby cool the inverter drive 46A. In one embodiment, when the compressor 48 is in the on cycle of the bump start mode, it operates at over 3000 revolutions per minute for 5 seconds and when the compressor 48 is in the off cycle it operates at 0 revolutions per minute for 15 seconds.

If query block 220 determines the inverter drive is the air cooled inverter 46B, the method 200 proceeds to query block 230 which determines if the inverter temperature exceeds the temperature limit minus the temperature offset by a predetermined temperature value. Similar to query block 220, in query block 230 if the predetermined value (temperature interval) is in excess of about 10° F. (>5.6° C.) the method 200 goes to block 232 where the amount of power to the windings of the motor stator 54 is reduced to the lower power level. If the predetermined value (temperature interval) is between about 0° F. and 10°0 F. (0° C. and 5.6° C.), the method 200 goes to block 234 where the windings of the motor stator 54 are de-energized completely so that they do not produce heat within the compressor 48. In the embodiment shown in FIG. 6, the method 200 proceeds from block 234 to block 236, where the second air circulation device 36 is run to cool the inverter drive 46B and alleviate the overheat condition of the inverter drive 46B.

Method 200 proceeds from blocks 216, 224, 228, 232 or 236 to query block 238 where it is determined whether the compressor 48 is the coldest part of the refrigerant system 10A or 10B under altered criteria from query block 216. In query block 238, this inquiry is conducted by comparing the temperature sensed by the motor stator temperature sensor 58 or the internal compressor temperature sensor 62 to either the minimum outdoor air temperature used in block 216 plus a temperature offset and the minimum indoor air temperature used in block 216 plus a temperature offset. If the temperature within the compressor 48 is colder than either the minimum indoor air temperature plus the temperature offset or the minimum outdoor air temperature plus the temperature offset, than the compressor 48 is the coldest part of the refrigerant system 10A or 10B (for the purposes of block 238) and further stator heating to warm the compressor 48 is required. In one embodiment, the temperature offset for the outdoor air temperature is a temperature interval of about 40° F. (200/9° C.) and the temperature offset for the minimum indoor air temperature is a temperature interval of about 15° F. (75/9° C.). If the compressor 48 is not the coldest part of the refrigerant system 10A or 10B as determined by block 238, the method 200 proceeds to block 239 where it is indicated that the compressor 48 is not the coldest part of the refrigerant system 10A or 10B under the criteria of query block 238.

If the compressor 48 is the coldest part of the refrigerant system 10A or 10B as determined by block 238, or method 200 has passed through block 239, the method 200 proceeds to query block 240 where it is determined whether the inverter drive 46A or 46B is overheating. In particular, in query block 240 if the sensed inventor temperature is greater than the minimum inverter temperature used in block 208 and the sensed compressor temperature is greater than the minimum compressor temperature used in block 210 and block 239 indicates that the compressor 48 is not the coldest part of the refrigerant system 10A or 10B then the method 200 proceeds to block 242 where the windings of the motor stator 54 are de-energized completely so that they do not produce heat within the compressor 48. The method 200 moves from block 242 (or query block 240 if one of the criteria of that block is not met) to block 244 before returning back to block 202.

Method 200 represents one embodiment used to control refrigerant system 10A or 10B during the off mode that includes the warm up mode as discussed previously. In other embodiments, the control method maybe altered, for example, by elimination or addition of block steps, by changing the power levels used to heat the windings of the compressor, or by altering the temperature criteria utilized in one or more blocks. Additionally or alternatively, other sensors such as those of the sensor array 56 (FIGS. 1A, 1B, 2A, and 2B) can be used with the control method.

While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims. 

1. A refrigerant system adapted to reduce refrigerant migration therein, the system comprising: a compressor having a motor with motor windings, the motor windings responsive to control signals to selectively generate heat in a manner that does not turn the motor; and a controller that selectively energizes the motor windings to generate heat based on at least one of a monitored temperature or pressure to warm the compressor.
 2. The system of claim 1, wherein the controller is the system controller.
 3. The refrigerant system of claim 1, wherein the controller determines a length of time during which the compressor has been inoperable and then calculates an operational time period to energize the motor windings to generate heat and/or the amount of heat desired to be generated by the motor windings based on the length of time the compressor has been inoperable.
 4. The refrigerant system of claim 1, wherein the controller calculates an operational time period during which the motor windings generate heat and/or an amount of heat desired to be generated by the motor windings based on at least one of the monitored refrigerant system temperature or pressure.
 5. The refrigerant system of claim 4, wherein the controller determines a length of time during which the compressor has been inoperable and then calculates the operational time period to energize the motor windings to generate heat and/or the amount of heat desired to be generated by the motor windings based on the length of time the compressor has been inoperable.
 6. The refrigerant system of claim 1, wherein the monitored refrigerant system temperature or pressure comprises at least one of a sensed outdoor air temperature, an outdoor coil temperature, an outdoor suction temperature, an indoor air temperature, an indoor unit return air temperature, an outdoor suction pressure, a motor stator temperature, an inverter drive temperature or an internal compressor temperature.
 7. The refrigerant system of claim 6, wherein the controller monitors the inverter drive temperature and the internal compressor temperature and selectively energizes the motor windings to generate heat based on whether at least one of the inverter drive temperature and the internal compressor temperature is less than at least one of a minimum indoor air temperature, a minimum outdoor air temperature, a minimum inverter drive temperature and a minimum internal compressor temperature.
 8. The refrigerant system of claim 7, wherein the controller monitors the inverter drive temperature and the internal compressor temperature and restricts the compressor from operating and energizes the motor windings to generate heat until the inverter drive temperature and the internal compressor temperature exceed predetermined temperatures.
 9. The refrigerant system of claim 7, wherein the controller monitors the inverter drive temperature and the internal compressor temperature at predetermined time increments based on the monitored outdoor air temperature.
 10. The refrigerant system of claim 6, further comprising a controller subassembly that monitors at least one of the motor stator temperature, the inverter drive temperature or the internal compressor temperature and selectively energizes the motor windings based on the at least one of the motor stator temperature, inverter drive temperature, or internal compressor temperature.
 11. The refrigerant system of claim 6, wherein the controller monitors the inverter drive temperature and cycles off or reduces current to the motor windings to maintain the inverter drive temperature below a predetermined temperature when the compressor is inoperable.
 12. The refrigerant system of claim 1, further comprising an inverter drive and wherein the inverter drive is refrigerant cooled and the controller operates the compressor at a minimum speed to allow for refrigerant to flow through and cool the inverter drive.
 13. The refrigerant system of claim 1, wherein the refrigerant system is configured as a heat pump, the heat pump comprising: a first heat exchanger in fluid communication with the compressor; a first air circulation device positioned adjacent the first heat exchanger; a second heat exchanger in fluid communication with the compressor and the first heat exchanger; a second air circulation device positioned adjacent the second heat exchanger; a reversing valve fluidly coupled between the first heat exchanger and the second heat exchanger; an electronic expansion device fluidly coupled between the first heat exchanger and the second heat exchanger; and an inverter drive; wherein the controller selectively energizes the motor windings to generate heat in a manner that does not turn the motor.
 14. The refrigerant system of claim 13, wherein the controller controls at least one of the first air circulation device and the second air circulation device to render at least one temporarily operable to selectively cool the inverter drive from an overheat condition that can result from the motor windings generating heat within the compressor.
 15. The refrigerant system of claim 13, further comprising: an outdoor suction pressure sensor and an outdoor suction temperature sensor disposed adjacent the reversing valve or an accumulator and configured to output the outdoor suction pressure and the outdoor suction temperature to the controller; a motor stator temperature sensor positioned within the compressor adjacent the motor windings and configured to output the motor stator temperature to the controller; an inverter drive temperature sensor positioned within the inverter drive and configured to output the inverter drive temperature to the controller; and an internal compressor temperature positioned within the compressor adjacent a compression area therein and configured to output the internal compressor temperature to the controller; wherein the controller selectively energizes the motor windings to generate heat to warm the compressor based on at least one of the outdoor suction temperature, inverter drive temperature, the internal compressor temperature, or the motor stator temperature.
 16. A method of reducing refrigerant migration to a compressor comprising: providing compressor having a motor with motor windings responsive to control signals to selectively generate heat in a manner that does not turn the motor; monitoring at least one of a refrigerant system temperature or pressure; and controlling the motor windings to selectively generate heat based on at least one of the monitored temperature or pressure to reduce refrigerant migration to the compressor.
 17. The refrigerant system of claim 16, wherein the controller is the system controller.
 18. The method of claim 16, wherein the monitored refrigerant system temperature or pressure comprises at least one of a sensed outdoor air temperature, an outdoor coil temperature, an outdoor suction temperature, an indoor air temperature, an indoor unit return air temperature, an outdoor suction pressure, a motor stator temperature, an inverter drive temperature or an internal compressor temperature.
 19. The method of claim 18, wherein the controller monitors the inverter drive temperature and the internal compressor temperature and selectively energizes the motor windings to generate heat based on whether at least one of the inverter drive temperature and the internal compressor temperature is less than at least one of a minimum indoor air temperature, a minimum outdoor air temperature, a minimum inverter drive temperature and a minimum internal compressor temperature.
 20. The method of claim 18, further comprising an inverter drive electrically connected to the compressor and configured to vary the speed of the compressor, and wherein the controller monitors the inverter drive temperature and either cycles off or reduces current to the motor windings to maintain the inverter drive temperature below a predetermined temperature or operates the compressor at a minimum revolution per minute or operates a fan adjacent to the inverter to allow for cooling of the inverter drive while the motor windings generate heat. 